Major advances in speech therapy for patients with Parkinson's disease (PD) have been made in the last decade. Significantly improved therapy results have been reported using the Lee Silverman Voice Treatment (LSVT) program. A core feature of LSVT is to instruct the patient to speak more loudly, thereby increasing sound pressure level (SPL). The general goal of this project is to investigate the physiologic mechanisms underlying increased SPL in patients with PD. Individuals with PD demonstrate speech movements (kinematics) which differ from normal speakers. It has been hypothesized that, in individuals with PD, increasing SPL causes a scaling-up of motor output from all three speech subsystems - respiratory, laryngeal, and articulatory - resulting in more normal speech production. The first specific aim of this project is to examine respiratory and articulatory kinematics in individuals with PD while they increase SPL. Individuals with PD may have difficulty accurately perceiving their own vocal intensity. Due to this difficulty, the mechanisms individuals with PD use to increase SPL may depend on the amount of self-monitoring of vocal intensity required by the task. Thus, the second specific aim of this project is to examine the effect of different cues to increase SPL on the kinematic mechanisms utilized by individuals with PD. Studies of motor control of the limbs have indicated that individuals with PD may have difficulty with premotor planning. If increasing SPL results in global effects to the speech system, as has been hypothesized, premotor organization may be altered. Therefore, there is one exploratory aim in the present project: to examine premotor planning of the respiratory subsystem for speech by individuals with PD. Methods employed in this project will include the collection and analysis of chest wall, lip, and jaw kinematics to examine the mechanisms for increasing SPL in individuals with PD. An understanding of the effects of increasing SPL on speech kinematics and premotor planning and of how difficulties in perception of vocal intensity affect kinematics is likely to assist with the improvement of speech therapy for individuals with PD and to further the understanding of the effects of PD on speech motor control.